Invoke-RestMethod で JSONをPOSTする
Invoke-RestMethod -Uri ($api+'/hoge') -ContentType 'application/json' -Method Post -Body ( @{"fuga"="puga"} | ConvertTo-Json)
Invoke-RestMethod -Uri ($api+'/hoge') -ContentType 'application/json' -Method Post -Body ( @{"fuga"="puga"} | ConvertTo-Json)